Plant Parenting: Optimum Temperatures for Seed Germination

Seed Germination Temperatures

It's that time of winter where many of you may be starting seeds indoors. Both air and soil temperature affect the speed and success rate of seed germination and growth. Each type of plant has a different optimal temperature range, based on its natural environment. Be sure to check the seed packet for specific optimal temperature ranges for germination.

Different types of seed will germinate faster than others. This basil ‘Genovese’ (below) is clearly an overachiever, when compared to the slower tomato and pepper seeds sown at the same time.

Many seeds germinate well in the 68°F to 80°F (20–26.6°C) range for both soil and air temperature. If temperatures are too cold or too warm, some seeds take a very long time to germinate or may not germinate at all.

If you want to speed up germination, or are starting seeds in a cold room or garage, try using a seedling heat mat, that goes under your seedling tray. Seedling heat mats can warm the soil or growing media temperature about 10-15°F. You can also purchase controllable thermometers for your heat mats.